HPHT In-Situ Strain Measurement of Polymer Composites for Oilfield Applications

Abstract

In recent years composite materials have been used extensively for drillable and other tools in oilfield operations because of their light weight, longer fatigue life, corrosion resistance and cost effectiveness. This requires determining their mechanical properties in such downhole conditions. Downhole tools are typically exposed to hot-wet environments above 93 °C (200 °F) and 34 MPa (5000 psi). Conventional environmental test methods conduct post-conditioning mechanical tests in dry conditions under ambient pressure, where the test condition is untrue and often giving misleading results. A previous publication presented an in-situ strain-gage measurement method using conventional resistive strain gages to determine the tensile strain and modulus of the composites in immersed hot-wet environment. However, satisfactory results were obtained only up to 93 °C (200 °F). This paper presents a new in-situ strain measurement technique, where an AC excited Wheatstone bridge with inductors is used. Thus, the sensor can operate as long as the inductors can resist the environment. Materials for the inductors were carefully selected to withstand how-wet conditions. The objective is to obtain the high-pressure-high-temperature (HPHT) in-situ tensile strain and tensile moduli of selected composite materials without discontinuing the hot-wet exposure cycle. Effect of the hydrostatic pressure on the tensile properties of the composites in hot-wet condition is presented.